An electrodeless fluorescent lamp is disclosed in U.S. Pat. No. 4,727,294 (U.S. Philips Corporation). The lamp of U.S. Pat. No. 4,727,294 comprises an externally spherical lamp vessel which is sealed and which contains a fill capable of sustaining a discharge when suitably excited. The discharge excites a phosphor coating on the inside of the vessel. The fill is excited by a core of magnetic material surrounded by a winding which is energized by a high frequency oscillator. The core and winding extend into a cylindrical sealing member of the vessel which extends into the spherical vessel. The lamp vessel is further provided with a light transparent, electrically conductive layer within the vessel to substantially confine the electric field generated by the core and winding within the vessel.
In order to reduce conducted interference, a portion of the external surface of the vessel is also provided with a conductive coating capacitively coupled to the conductive layer inside the vessel. The external coating is connected by a conductor to a power mains terminal of the lamp.
An electrically insulative, generally cylindrical, housing supports the spherical lamp vessel and the re-entrant sealing member. The housing has a diameter much smaller than the spherical lamp vessel. The housing contains the oscillator circuit and mechanically connects the lamp vessel to the lamp cap. The portion of the external surface of the vessel which is provided with the conductive coating is inside the housing.
Although U.S. Pat. No. 4,727,294 achieves an advance over the prior art in terms of reducing EMI characteristics of an electrodeless fluorescent lamp, there is still a need to further reduce EMI emissions so as to reach compliance with appropriate governmental standards relating to EMI emissions. Moreover, such patent further could be improved if the teaching contained therein could be extended to other lamp configurations rather than just the conventional A-line configuration. Accordingly, it would be advantageous if an electrodeless fluorescent lamp could be provided that would further improve EMI suppression properties as compared to known lamps of this type and further, could be applied to different lamp configurations such as a reflector lamp for instance.